Factors causing stepping motor out of step and preventive measures
Stepper motor can realize open-loop control of position and speed of motor according to pulse number and pulse frequency. It is a cheap, simple and easy-to-use control motor, which is more and more widely used in the field of automatic control. However, because the stepper motor is not closed-loop control, improper selection or use will also easily lead to step loss of the stepper motor, which is also called step loss of the stepper motor, that is, the stepper motor does not reach the position it should reach according to the instructions, which makes the engineers very distressed. Then, what is the reason for stepping motor out of step? What countermeasures can be taken to avoid out of step?
There are many reasons for stepping motor out of step. In the process of practical application, it is necessary to take the elimination method to analyze one by one in order to find out the real reason for stepping motor out of step. Generally, the reasons for stepping motor out of step are as follows:
1. The working torque of the stepping motor itself is not enough, and it does not have enough capacity to drive the load;
2. The acceleration and deceleration process of starting and stopping of stepping motor is insufficient, and the stepping motor loses step in the acceleration and deceleration process;
3. Insufficient power supply of stepper motor leads to insufficient input power of stepper motor, resulting in out of step;
4. The driving voltage of stepping motor is not enough or the driving current is set too low;
5. The driver or controller receives signal interference;
6. The step motor system resonance causes the step motor to reduce the load capacity and lead to out of step;
7. The signals of driver and controller do not match;
8. The back clearance of the synchronous wheel or reduction gearbox or the clearance error of turning back and forth is not compensated in the program or the compensation value is incorrect;
9. There is a problem with the control procedure itself.
It should be familiar to engineers in the electrical control industry to start into the motor! Its error will not accumulate for a long time, it can realize accurate positioning, and the control is simpler than servo. However, the premise of accurate control of stepping motor is that the motor does not lose step. How can we avoid the step loss of stepping motor?
Stepper motor is an open-loop control motor that converts electric pulse signal into angular displacement or linear displacement. In the case of no out of step, the speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal, and are not affected by the load change. When the stepping motor receives a pulse signal, the motor rotates a fixed angle (step angle or step angle) according to the set direction, and the angular displacement and speed of the motor are controlled by controlling the number of pulses and pulse frequency, so as to achieve accurate open-loop control. In addition, there is always a certain error between the rotation angle of each step of the stepping motor and the theoretical step distance, and there is always a certain error from a certain step to any step. However, the number of steps per cycle of the stepping motor is the same, and its step distance error does not accumulate for a long time without losing step.
How to avoid the situation mentioned above? First of all, we need to know the factors causing motor out of step:
1. The rotor acceleration is slower than the rotating magnetic field of stepping motor;
2. The average speed of the rotor is higher than the average rotation speed of the stator magnetic field;
3. The load inertia of the motor is large;
4. The stepping motor resonates.
The rotor acceleration is slower than the rotating magnetic field of the stepping motor, that is, when the rotor speed is lower than the commutation speed, the motor will be out of step. This is because the electric energy input to the motor is insufficient, and the generated torque can not make the rotor speed keep up with the rotating speed of the stator magnetic field, resulting in out of step. The average speed of the rotor is higher than the average rotation speed of the stator magnetic field, which means that the stator is energized and excited for a long time, which is greater than the time required for stepping. The rotor obtains too much energy in the stepping process, resulting in too large torque generated by the motor, resulting in the stepping of the motor.
The above causes of stepping motor out of step are actually caused by improper selection of stepping motor driver. Only by selecting the correct and appropriate stepping driver can the stepping motor give full play to its advantage of accurate control. Selecting a suitable driver requires a driver greater than or equal to this current according to the current of the motor. If low vibration or high precision is required, it can be equipped with subdivision driver. For high torque motors, high voltage drives should be used as much as possible to obtain good high-speed performance. At the same time, for the driving power supply, many people directly use the switching power supply as the driving power supply. However, it is generally best not to use the switching power supply, especially the high torque motor, unless the switching power supply with more than twice the required power is selected. Because when the motor works, it is a large inductive load, which will form an instantaneous high voltage on the power supply end. The overload performance of switching power supply is not good, which will protect and turn off, and its precise voltage stabilizing performance is not needed, which may sometimes cause the damage of switching power supply and driver. For the driving power supply of stepping motor, conventional ring or R-type transformer variable voltage DC power supply can be used.
The reason why the stepping motor resonates is that the pulse frequency received by the motor is equal to the natural frequency of the stepping motor, which is related to the subdivision of the driver. When we generally use stepping motor, the subdivision ability of the driver is very important. The smaller the resonance range, the better. The large load inertia of the motor is caused by the overload of the motor, so it can be avoided only by paying attention not to overload the motor.